Songbird's duets not so harmonious

Image: Rufous-and-white wren
Some birds, such as the rufous-and-white wren pictured here, fight by singing, using melodic tweets to defend their relationships and territoriesDaniel Mennill
/ Source: Discovery Channel

Harmonious bird songs may sound pleasant to people, but a new study has found that at least some birds fight by singing, using melodic tweets to defend their relationships and territories.

The study, published in the latest issue of Current Biology, was made possible by eight microphones positioned strategically throughout the dense tropical forests of Costa Rica. The microphones fed the song duets of rufous-and-white wrens into a single laptop computer, enabling researchers to pinpoint the exact positions of the colorful songbirds.

"The first time I heard a rufous-and-white wren song, I was completely captivated by its voice," lead author Daniel Mennill told Discovery News. "They have low-pitched, flute-like sounds that are really quite beautiful."

Mennill, an associate professor in the Department of Biological Sciences at the University of Windsor, and colleague Sandra Vehrencamp conducted two experiments on breeding pairs of the birds, which can sing such closely matched duets that human listeners think they're hearing a solo performance.

They first recorded the birds in a passive context.

"This is analogous to recording you as you go about your daily routine of making your lunch, tidying your house, etc.," explained Mennill.

The bird pairs used duets to find each other, like a romantic B movie where the male and female stars sing out to one another while moving ever closer. Given the density of the birds' forest home, such singing is one of the few ways males and females can find each other.

For the second experiment, the scientists recorded the birds in a more aggressive context. Using loudspeakers, they simulated the voices of a rival pair.

"This is analogous to recording you if you were reacting to a burglar breaking into your house," Mennill said.

When a bird pair would hear a rival couple singing, the "birds' duet rates skyrocketed."

The listening couple "duetted intensely and approached the loudspeakers aggressively," Mennill said, with males singing loudly and forcefully when they heard a rival male tweet.

The researchers believe the bird couples sing duets to not only protect their territories from rival couples, but also to prevent other birds from disrupting their relationship. Extra-pair matings have been documented in this species and most other birds.

"Moreover, rufous-and-white wrens frequently engage in divorce," the authors point out.

They believe their findings apply to many other birds that sing duets, particularly those living in areas of thick vegetation.

Herman Mays Jr., curator of zoology at the Geier Collections and Research Center at the Cincinnati Museum Center, told Discovery News that the new "paper is a very important contribution, not just to the literature on avian duetting, but towards our understanding of animal communication in general."

Mays said the innovative eight-microphone system is already "proving to be a critical tool in studying animal behavior."

He was also glad to see a paper addressing the apparent double meaning of certain bird songs, which can bring avian couples together and keep rivals at bay. The issue, he said, has been a "very interesting puzzle in animal communication" for many years.